Dicing

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Dicing
Cutting-Substrate.jpg
Technology Details
Technology Packaging
Equipment List of dicing equipment
Materials %Optional materials processed%
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Dicing is the process by which die are separated from a wafer of semiconductor following the processing of the wafer. The dicing process can be accomplished by scribing and breaking, by mechanical sawing with a dicing saw or by laser cutting. All methods are typically automated to ensure precision and accuracy.

Method of operation

Differentiate dicing v. scribing (and why you would use each)

Dicing saw

Wafers are typically mounted on dicing tape which has an adhesive backing that holds the wafer on a metal frame. The frame with the wafer on it is placed on the chuck of the dicing saw. The wafer is moved into an abrasive blade, usually diamond, rotating at typically 15,000 to 30,000 RPM. The abrasive chips away at the wafer as the blade rotates. Water is supplied to the blade to remove cutting residue and enhance cut quality.

Scribing

A scribe, typically diamond, is in contact with and moved across the wafer along crystal plane (if present) with enough pressure to make a scratch on the surface. The wafer is then broken at the scribe line by applying pressure to the back side of the wafer, bending the wafer. The scribe and break method can process wafers faster than sawing without any residual stress or the use of cooling water.

Applications

Dicing is typically used to separate die from a wafer to be mounted in a package or on a PC board. Some users dice a wafer into smaller pieces to process individually. These wafers should be protected from dicing contaminants.

It can be used to cut a wide range of materials and devices including Semiconductor devices, Ceramic Substrates, Thick-film Devices, Glass on Silicon (Sensors), SAW Filters, MEMS, Package Singulation (BGA, QFN, LTCC, LED packaging), Opto-electronic Components, IC Wafers. For other applications, we can consult blade manufacturers for recommendations. For a list of commonly diced materials, see the materials section.

Other uses are custom shaping, scribing and grooving.

Parameters

Blade

There are many dicing blade parameters. Here are a few.

  • Thickness
    The thickness of the blade should be less than the desired kerf width. Blade thickness also depends on the material being cut and the blade exposure. More exposure requires a thicker blade.
  • Exposure
    Blade exposure should be greater than the depth of the cut (including 25 µm when cutting through the wafer into the mounting tape) plus at least 100 µm for a safety margin and efficient exiting of the slurry waste.
  • Bond hardness
    The hardness of the bonding material is critical to insure prolonged blade wear and the self-sharpening mechanism of the blade. When the bonding matrix is too soft, the blade will wear too fast. Too hard an edge can result in blade "loading" which can introduce more chipping.[1]. Aluminum requires a softer bond hardness to prevent the material from collecting in the blade, causing it to break.
  • Grit size (Mesh Size)
    Diamond size in microns or in mesh. Larger diamonds are better suited to cutting very hard materials. Smaller diamonds give a higher quality cut.
  • Diamond concentration
    Higher diamond concentration causes the blade to act harder and wear slower. Hence, higher diamond concentration is recommended and usually used for cutting softer and more abrasive types of materials. However, the trade off is significantly slower cutting speed. Since there is higher density of diamond particles in bond matrix, there is not enough space for the debris and fine powder created during dicing process to escape. Blade overloading is often a result of selecting improper diamond concentration.
    Low diamond concentration dicing blade is softer and faster wearing blade, creating better cut quality and surface finish. Low diamond concentration is often recommended and widely used for cutting ultra hard and brittle materials. Lower diamond concentration has larger spacing between diamond particles and can accept more fine powder debris generated from dicing.[2]
  • Binder
    The matrix material holding the diamonds.
    Some common binder materials are Nickel, Phenolic resin, and Metal-powder sintered.

Feed rate

The rate at which the wafer is moved into the blade or under a scribe.
Feed rate should be determined by your desired cut quality, material hardness, density, and thickness. Most dicing operations require cutting as much material as possible, in shortest period of time possible. Frequently most gains in cutting speed and output are done at the expensive of cut quality. You should maintain the feed rate best suited for your required cut quality. Too high feed rates can also cause excessive chipping and material cracking, increasing die rejection rates.[3]

Spindle speed

The rate that the saw blade is rotated in revolutions per minute.
Low spindle RPM’s will cause the blade to wear faster to maintain better cut quality. Causing softer dicing action, where each diamond particle grinds out a larger portion of material. This will result in higher blade wear but will expose new, fresh diamonds, resulting in a cleaner cut. Higher spindle RPM’s will do the opposite. Each diamond particle will grind away a small portion of material, creating harder dicing action.[3] [4]

Depth

The distance from the chuck that the blade is positioned during cutting. It could also be the distance from the top of the wafer. Can also apply to a scribe tool. Cut depth is, in most cases, a function of the substrate thickness. It should be optimized depending on the cut quality and blade loading. [4] A good rule of thumb is to cut no more than about 500 µm of material per pass. Harder materials should be cut with shallower cuts and more passes to minimize blade wear. Deeper cuts require a thicker blade to minimize blade flexing or deflection.

Index

The distance between cuts or scribes. The die size will be the index minus the kerf.

Scribe pressure

The amount of pressure placed on a scribe tool when moving across a wafer.

Figures of merit

Kerf

The gap or space between singulated die as a result of saw dicing. The width of the kerf is approximately equal to or slightly greater than the width of the dicing saw blade. [5]

Edge chipping

The chipping size is defined as the width measured from the kerf line to the die edge of spalling (chip) [6]

Materials

Some of the materials that can be diced are Alumina, Aluminum, BiTe, Ceramics, Fused silica, Gallium arsenide (GaAs), GaN, GaP, Glass, InSb, Lithium niobate, PZT, Quartz, Sapphire, SiC, Silicon, Stainless Steel. Some of these materials require a special blade.

Equipment

Below is a general description of the Dicing equipment at the LNF.

ADT 7100 Dicing Saw

Main article: ADT 7100 Dicing Saw

The ADT 7100 Dicing Saw is optimized for multi-angle dicing of thin, tight tolerance products up to 150 mm or 6" diameter. It is capable of more complex patterns such as multiple indexes and varying cut depths.

See also

Other related wiki pages

References

  1. Area Array Interconnection Handbook, Karl J. Puttlitz, ‎Paul A. Totta - 2012[1]
  2. Selecting right diamond dicing blade for your application[2]
  3. 3.0 3.1 Dicing Blade Operation Recommendations[3]
  4. 4.0 4.1 Process Optimization of Dicing Microelectronic Substrates By Gideon Levinson[4]
  5. KerfAid Dicing Fluid - Definitions & FAQ[5]
  6. Investigation of chipping and wear of silicon wafer dicing[6]

Further reading

[[Category:{{|var:acronym|{{PAGENAME}}}}]] [[Category:Packaging][:ADT 7100 Dicing Saw]]